The present invention relates to a tool chuck, and more particularly relates to improvement in construction of a chuck for firmly holding a tool such as a drill bit or a driver bit of electric work devices by means of three or more clamping jaws.
One typical example of such a tool chuck is proposed in Japanese Utility Model Laid-open Sho. 63-189509. The tool chuck of this earlier application includes a tubular chuck body which slidably accommodates a plurality of clamping jaws in its front section in a coaxial and forwardly converging arrangement. Each clamping jaw is kept in outward screw engagement on its proximal section with a screw ring which is in an annular cutout formed in the intermediate section of the chuck body. This screw ring is in turn kept in screw engagement with an operation sleeve idly inserted over the chuck body for manual operation.
As the operation sleeve is manually rotated, the screw ring is driven into concurrent rotation in the clamping direction which in turn causes convergent, collective forward sliding of the clamping jaws via screw feeding to hold a tool inserted into the center section of the chuck body. As the jaws clamp the tool, reaction from the tool is transmitted to the screw ring via the clamping jaws and the screw ring is force to move rearwards. As a result, the rear face of the screw ring is brought into tight pressure contact with the rear side wall of the annular cutout in the chuck body.
This pressure contact generates friction resistance against rotation of the screw ring within the annular cutout. As a result, a great deal of input torque from the operation sleeve is consumed to overcome this friction resistance without effectively producing high degree of clamping force on the tool. In other word, input torque from the operation sleeve is greatly wasted without effective utilization.